1. Field of the Invention
The present application claims priority from Japanese Patent Application No. JP 2008-107486 filed in the Japanese Patent Office on Apr. 17, 2008 and Japanese Patent Application No. JP 2008-190601 filed in the Japanese Patent Office on Jul. 24, 2008, the entire contents of which are incorporated herein by reference.
The present invention relates to a surface light source device irradiating light and an image display device using the same.
The present invention relates to a surface light source device irradiating light and an image display device using the same.
2. Description of the Related Art
There exists a surface light source device performing illumination by using light sources such as a cold cathode fluorescent lamp (CCFL) and a light emitting diode (LED). The surface light source device is used for, for example, lighting equipment by using the light source as illumination directly, or used for image display devices such as a television receiver and a personal computer by using the light source as backlight illumination.
As the above image display device, for example, a liquid crystal display device using a liquid crystal panel as a display panel on which images are displayed can be cited. Since the liquid crystal panel is not a self-luminous type display in the liquid crystal display device, a surface light source device irradiating light from the back surface side with respect to the liquid crystal panel is disposed. In this case, the surface light source device is used as a backlight device irradiating light to the liquid crystal panel from the back surface side.
In the surface light source device used as the backlight device, there are a device called as a side-edge type and a device called as a direct-method type. The side-edge type surface light source device includes a light guide member as well as a light source disposed at the side of the light guide member, which irradiates light to the display panel by guiding light emitted from the light source by the light guide member to a given direction. The direct-method type surface light source device includes light sources disposed at the back surface side of the display panel, which irradiates light emitted from the light sources to the display panel. In a liquid crystal display device used as a television receiver and a large-sized liquid crystal display device, the direct-type backlight device is mainly used as the surface light source device because it is necessary to obtain bright images.
The surface light source device used for the liquid crystal display device commonly includes a diffusing member (a diffusing plate or a diffusing sheet) arranged facing the back surface of the liquid crystal panel and a reflective member arranged at the back surface side of the diffusing member. In the surface light source device, for example, plural fluorescent lamps such as cold cathode fluorescent lamps used as light sources are arranged in a state aligned in a given direction, and the diffusing member is arranged between the fluorescent lamps and the display panel. The diffusing member has a function of avoiding visual recognition of outer shapes of the fluorescent lamps through the display panel and avoiding recognition of existence of the fluorescent lamps as lamp images by the user by diffusing light emitted from the fluorescent lamps and irradiating light to the display panel uniformly. The diffusing member also has a function of irradiating light emitted from light sources to the liquid crystal panel uniformly to secure uniformity of luminance of a display screen in the liquid crystal panel.
In the liquid crystal display device, when light is emitted from light sources, the emitted light is diffused by the diffusing member and irradiated to the liquid crystal panel on which an image is displayed from the back surface side. At this time, light is emitted from the light sources not only to the diffusing member side but also to the reflective member side. The light emitted to the reflective member side is reflected by the reflective member and incident on the diffusing member, then, the light is diffused by the diffusing member and irradiated to the liquid crystal panel.
In the liquid crystal display device as described above, the demand for a thinner device is extremely high. As a method for obtaining the thinner device, a method of shortening distance between light sources and the diffusing member can be considered. However, when the distance between light sources and the diffusing member is shortened, the existence of lamps as described above tends to be recognized as lamp images.
Accordingly, a surface light source device disclosed in, for example, JP-A-2006-162827 (Patent Document 1) is proposed, in which a member called as a prism array is disposed between light sources and the diffusing member and light irradiated just above the light sources is reflected by the member to reduce luminance just above the light sources, as a result, the recognition as lamp images is reduced. Another approach for improving uniformity by arranging a light control member which is an arrangement structure of a lens between the reflective member and light sources is performed. Specifically, for example, in JP-A-2007-80747 (Patent Document 2), a surface light source device in which the light control member on the reflection sheet is allowed to be a fresnel-lens shape and light is condensed between the light sources to reduce the recognition of the lamp images is proposed. Additionally, for example, in U.S. Patent Application Publication No. 2005/0141212 (Patent Document 3), a surface light source device in which the light control member on the reflection sheet is allowed to be a circular shape and the diffusing function is improved to reduce the recognition of the lamp images is proposed. Also, in JP-A-10-283818 (Patent Document 4), a surface illuminant in which a lens sheet having linear protrusions is disposed between the light sources and the reflection plate is disclosed.